1. Field of the Invention
The present invention relates to motion detectors, and more particularly, to a microwave transceiver capable of detecting motion within a spatial region extending substantially radially outward and 360.degree. in azimuth with respect thereto.
2. Description of the Related Art
Area protection sensors and/or intrusion detection systems, such as those used in burglar alarms, typically include presence and/or motion detectors. Two general types of detectors are used: passive and active. An example of a passive detector is a passive infrared detector which detects the presence and/or motion of infrared radiation within a defined area to be protected.
An example of an active detector is a transceiver. The transceiver transmits and receives some form of radiation to detect the presence and/or motion of an object within the defined area to be protected. One example is an acoustic transceiver which transmits and receives acoustic radiation (e.g., ultrasonic, SONAR) to perform its detection function. Another example is a microwave transceiver which transmits and receives microwave radiation (typically frequencies greater than 1 Gigahertz) to perform its detection function.
In a microwave transceiver, the microwave radiation is typically coupled into free space and transmitted by way of a waveguide horn antenna. (See FIG. 1.) Such an antenna effectively radiates and collects the microwave radiation, however, its radiation dispersion and collection characteristics are not omni-directional. In fact, such an antenna exhibits a high degree of directivity, i.e., the edges of its radiation dispersion/collection characteristics extend outwardly at an acute mutual angle. Thus, such a waveguide antenna is limited to less than 180.degree. of coverage in the azimuth.
Although other types of antennas may be used to obtain an omni-directional radiation dispersion/collection pattern, typically they require additional external parts making them larger, more expensive and difficult to align/tune. For example, a reflector type of antenna may be used. But, such an antenna is typically significantly larger and does not provide uniform field strength within the radiated wave. As another example, a multiple element, or array, type of antenna may be used. However, such an antenna is significantly larger with tighter fabrication tolerances and requires a complex signal feeder.